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hooks/setup00-merged-usr.sh: add rationale

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Johannes Schauer Marin Rodrigues 2021-02-04 17:40:35 +01:00
parent 4e658549f0
commit aaa7c14275
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hooks/setup00-merged-usr.sh
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@ -1,4 +1,33 @@
#!/bin/sh
#
# mmdebstrap does have a --merged-usr option but only as a no-op for
# debootstrap compatibility
#
# Using this hook script, you can emulate what debootstrap does to set up
# merged /usr via directory symlinks, even using the exact same shell function
# that debootstrap uses.
#
# mmdebstrap will not include this functionality via a --merged-usr option
# because there are many reasons against implementing merged-/usr that way:
#
# https://wiki.debian.org/Teams/Dpkg/MergedUsr
# https://wiki.debian.org/Teams/Dpkg/FAQ#Q:_Does_dpkg_support_merged-.2Fusr-via-aliased-dirs.3F
# https://lists.debian.org/20190219044924.GB21901@gaara.hadrons.org
# https://lists.debian.org/YAkLOMIocggdprSQ@thunder.hadrons.org
# https://lists.debian.org/20181223030614.GA8788@gaara.hadrons.org
#
# In addition, the merged-/usr-via-aliased-dirs approach violates an important
# principle of component based software engineering one of the core design
# ideas/goals of mmdebstrap: All the information to create a chroot of a Debian
# based distribution should be included in its packages and their metadata.
# Using directory symlinks as used by debootstrap contradicts this principle.
# The information whether a distribution uses this approach to merged-/usr or
# not is not anymore contained in its packages but in a tool from the outside.
#
# The problem is not the idea of merged-/usr but the problem is the way how it
# got implemented in debootstrap via directory symlinks. That way of rolling
# out merged-/usr is bad from the dpkg point-of-view and completely opposite of
# the vision with which in mind I wrote mmdebstrap.
set -exu